Integrated circuits (ICs) and other electronic devices are commonly packaged in so-called IC chip carriers. A chip carrier comprises a body of insulating material having the IC chip contained therein. The chip carrier has contact areas located at predetermined spaced locations near its periphery, the spaced locations correspond to the spaced locations of conductive areas of the substrate.
As technology in this area is advanced, and ICs become more complex, IC chip carriers and substrates are required to have high numbers of closely spaced contacts or conductive areas positioned thereon. With this type of technology being developed, a problem arises. It is hard to ensure that a positive electrical connection is effected between the high density, relatively small conductive areas of the substrate and the high density, relatively small contact areas of the chip carrier. Consequently, transition sockets, such as those described in U.S. Pat. No. 4,699,593, have been utilized to provide the electrical path required between the chip carrier and the substrate.
The dimensions of the chip carriers and sockets are so small that any damage to the leads of the chip carrier will result in an unstable and unreliable electrical connection. Therefore, it is important to protect the contact areas of the chip carrier during transportation and handling, to ensure that the numerous, very closely spaced contact areas are positioned in the correct locations when testing or installation is to occur. An example of the type of protective handler used is described in U.S. patent application, Ser. No. 926,024, filed Oct. 31, 1986.
The protection of the contact areas ensures that the contact areas will be maintained in their proper position. However, an unstable and unreliable electrical connection can occur due to any minimal amount of deflection or warpage associated with the chip carrier, the contact areas, or the socket. Consequently, for a positive electrical connection to be effected between the contact areas of the chip carrier and the contact areas of the substrate, it is essential that adequate contact pressure be provided to overcome and eliminate the above mentioned problems. Pending U.S. patent application, Ser. No. 926,024, filed Oct. 31, 1986 describes one type of pressure plate which provides the contact pressure required to ensure that electrical connection is affected. However, the pressure plate described and claimed in that application has several problems associated therewith.
The configuration of the pressure plate described in the above referenced referenced patent application necessitates the use of a tool for installation and removal thereof. The use of a tool complicates the procedure which must be followed when installing or removing the pressure plate. This increases the time required for installation and removal, as well as adding to the complexity of the process by requiring a separate and distinct tool for proper operation.
The use of a tool for installation is more than just an inconvenience, damage to the substrate or test site can occur, rendering the substrate effectively useless. This damage can occur as a result of the operator overstressing the posts of the substrate. As the pressure plate is inserted onto the posts of the burn-in socket, etc., the operator must turn the pressure plate by means of the screw driver or the like. This rotation enables the openings of the pressure plate to cooperate with the posts of the socket in order to apply the contact pressure required to insure that a proper electrical connection has been made between the chip and the substrate. If this is done properly, a positive electrical connection is affected and the socket, etc. is not damaged. However, in the real world, the operator is likely to rotate the pressure plate more than is required, thereby ensuring that the pressure plate is secured in place. Over rotation of the pressure plate results in harmful stresses being applied to the posts, and consequently, to the substrate. This results in damage or failure of the substrate and/or the posts. particularly over the course of many cycles. This damage can be costly to repair, as the replacement of the entire substrate may be required.
Alternatively, the operator will not rotate the pressure plate far enough, resulting in an incomplete turn of the cover plate. This under rotation of the cover plate produces an inadequate contact pressure, which in turn results in an unreliable electrical connection between the substrate and chip carrier. This can lead to inaccurate results, which may result in good quality chips being wrongly discarded. Even if the contact pressure is sufficient, the pressure plate will be easily rotated out of position as testing occurs.
As neither of the conditions described above are desirable from a cost or reliability stand point, it would be beneficial to have a contact plate which will provide a fail safe way of generating the appropriate rotation and pressure to ensure that a positive electrical connection is effected. The ideal situation being one in which the cover plate is rotated with only minimal effort from the operator, thereby eliminating the possibility of human error. The present invention is directed to the achievement of such a device.